The 39-story tower was designed by Shreve, Lamb & Blake and built by Abraham Lefcourt in the crash year of 1929. It has been previously owned by Metropolitan Life, Larry Silverstein, Bernie Mendik and more recently RFR’s Aby Rosen and Michael Fuchs, who retained the land until last year when, under a prearrangement, they sold everything to SL Green for $225 million.

Since 2006, SLG has invested almost $30 million to transform the granite tower on the northeast corner of 43rd Street with a new entrance, contemporary lobby, elevators, halls, bathrooms, retail spaces, messenger center, security, cooling and other systems.

The 60,000 square feet of retail is now occupied by Equinox and Urban Outfitters. This stretch of Fifth Avenue just keeps getting more valuable as Joe Fresh, Zara, Tommy Bahama and H&M dress it up.

CoStar data and the building’s website show just a handful of office availabilities ranging from $55 a square foot for the entire 21,677-square-foot fifth floor to boutique tower floors for $65 a square foot.

Harmon and Spies also just completed the preemptive repurchase by Paramount Group of its investment partner Investa Office’s interest in 900 Third Ave. for $600 a square foot, sources said.

Because of its location, in-place cash flow — city estimates show net operating income at $11,473,513 — and worldwide focus on city properties, the investment stake in 521 Fifth is expected to sell closer to $650 to $700 per square foot.

Everyone declined comment, but stay tuned.

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Speaking of 900 Third, entertainment rights powerhouse CKX signed an 18,245 square foot deal for the entire 18th floor for the next 10 years.

Newmark Knight Frank’s Chris Mongeluzo and Corey Horowitz represented CKX in its relocation from two floors at 650 Madison Ave.

Peter Brindley repped the Paramount Group ownership in-house along with Doug Neye at Jones Lang LaSalle.

CKX represents the names and likenesses of Elvis Presley and Muhammad Ali along with the “American Idol” and “So You Think You Can Dance” brands. It was just bought by Apollo Global Management.

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Apologies to the city’s Department of Finance, which now does advise property owners when there are credits in the account histories.

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The New York City Opera will soon be singing the praises of downtown as it relocates to 16,936 square feet on the 10th floor of 75 Broad St.

The move will save significant rent as it qualifies for relocation benefits worth about $2 per square foot per year. Additionally, according to the building’s broker, Frank Cento of Cushman & Wakefield, “The spread between Midtown and downtown rents just exceeded $25.”

The asking rents at 75 Broad are now $33 to $35 a square foot.

The Opera, which now performs at the Brooklyn Academy of Music, was represented by Stephen Powers and Paul Wolf of Denham Wolf.

Another recent deal at 75 Broad was the relocation from 15 Maiden Lane and expansion of Craig Michaels into 10,200 square feet, which was represented by Mitch Waldman of Cogent Realty. On-Line Residential, represented by Ken Beilin of Kenneth Beilin Realty, will occupy 7,124 square feet in a move from 50 Broad, while CTC Americas, represented by Jonathan Fein of Cushman & Wakefield, will occupy 3,800 square feet in a slight expansion and relocation from 80 Broad.

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Minds In Sync leased an additional 3,771 square feet on the 17th floor to now total 16,000 square feet at 1350 Broadway. “The innovative home products company came to the building in 2010 on a 2,814 square foot sublease on the 4th floor and has kept growing,” said Abe Labaton of Vicus Partners.

Labaton represented the company in the latest deal.

Neil Rubin, Rob Silver and Anthony Sciacca of Newmark Knight Frank represented the Malkin Properties building, which has an asking rent in the mid-$40s.